U.S. patent application number 09/729431 was filed with the patent office on 2001-06-07 for wind-powered generator plant.
This patent application is currently assigned to Mitsubishi Heavy Industries, Ltd.. Invention is credited to Honda, Akihiro, Saito, Toru.
Application Number | 20010002757 09/729431 |
Document ID | / |
Family ID | 18394029 |
Filed Date | 2001-06-07 |
United States Patent
Application |
20010002757 |
Kind Code |
A1 |
Honda, Akihiro ; et
al. |
June 7, 2001 |
Wind-powered generator plant
Abstract
Windmill generator sets, each including a windmill and a
generator driven by the windmill, are installed on a floating body
floating on water. The floating body is formed as a triangular
truss structure. Each side of the triangle of the floating body is
formed by a hollow beam having a rectangular cross section. The
windmill generator sets are disposed on the floating body at the
respective corners of the triangle. The distance between the
centers of windmills, adjacent to each other, is set at a value
smaller than four times, preferably smaller than two times, the
diameter of the rotors of the windmills. By setting the distance
between the centers of the windmills at a value smaller than four
times of the rotor diameter, the construction cost of the floating
body can be reduced without any accompanying reduction in the power
generation efficiency of the windmill generator sets, whereby the
unit power generating cost of the plant can be reduced.
Inventors: |
Honda, Akihiro;
(Nagasaki-ken, JP) ; Saito, Toru; (Nagasaki-ken,
JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN, HATTORI,
MCLELAND & NAUGHTON, LLP
1725 K STREET, NW, SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
Mitsubishi Heavy Industries,
Ltd.
Tokyo
JP
|
Family ID: |
18394029 |
Appl. No.: |
09/729431 |
Filed: |
December 5, 2000 |
Current U.S.
Class: |
290/55 ;
290/44 |
Current CPC
Class: |
F05B 2250/12 20130101;
F05B 2240/93 20130101; F05B 2240/95 20130101; Y02E 10/72 20130101;
F05B 2240/40 20130101; E02B 2017/0091 20130101; F03D 13/25
20160501; F05B 2250/11 20130101; F03D 1/02 20130101; Y02E 10/727
20130101 |
Class at
Publication: |
290/55 ;
290/44 |
International
Class: |
F03D 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 7, 1999 |
JP |
11-347994 |
Claims
1. A wind-powered generator plant comprising a floating body placed
on water and a plurality of windmill generator sets disposed on the
floating body, wherein at least one pair of the windmill generator
sets are disposed on the floating body in such a manner that the
distance between the centers of the rotors of the windmills is less
than four times of the diameter of the rotors of the windmills.
2. A wind-powered generator plant as set forth in claim 1, wherein
said pair of the windmill generator sets is disposed in the
direction of wind.
3. A wind-powered generator plant as set forth in claim 1, wherein
the distance between the centers of the rotors of the windmills of
said pair of windmill generator sets is less than two times the
diameter of the rotors of the windmills.
4. A wind-powered generator plant as set forth in claim 2, wherein
the distance between the centers of the rotors of the windmills of
said pair of windmill generator sets is less than two times the
diameter of the rotors of the windmills.
5. A wind-powered generator plant as set forth in claim 3, wherein
the distance between the centers of the rotors of the windmills of
said pair of windmill generator sets is more than one and half
times the diameter of the rotors of the windmills.
6. A wind-powered generator plant as set forth in claim 4, wherein
the distance between the centers of the rotors of the windmills of
said pair of windmill generator sets is more than one and half
times the diameter of the rotors of the windmills.
7. A wind-powered generator plant as set forth in claim 1, wherein
the floating body is formed as a truss structure combining beams
having hollow cross sections.
8. A wind-powered generator plant as set forth in claim 6, wherein
the floating body is formed as a triangular truss structure and
each of three sides thereof is formed of a beam having a hollow
cross section.
9. A wind-powered generator plant as set forth in claim 7, wherein
the cross section of the beam is rectangular.
10. A wind-powered generator plant as set forth in claim in claim
8, wherein the cross section of the beam is rectangular.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an aerogenerator plant or a
wind-powered generator plant which utilizes wind power to generate
electricity. More specifically, the present invention relates to a
wind-powered generator plant having a plurality of generators,
driven by windmills, installed on a structure floating on
water.
[0003] 2. Description of the Related Art
[0004] An aerogenerator system or a wind-powered generator system
which converts the kinetic energy of windmills driven by wind power
into electricity is known in the art. A wind-powered generator
system is a "clean" electric generating system since it does not
require fuel for combustion. However, since a wind-powered
generator system requires a stable wind, availability of sites
suitable for constructing a wind-powered generator plant is rather
limited on the land.
[0005] On the other hand, since it is relatively easy to find a
site on water where a stable wind can be obtained, it is possible
to construct a wind-powered generator plant on water such as a lake
or the sea.
[0006] When a wind-powered generator plant is constructed in
shallow water, a wind-powered generator plant can be constructed as
a fixed type plant in which a substructure is constructed on the
lake bottom or sea bed and windmill generator sets are placed on a
superstructure constructed on the substructure. However, if the
water is deep, it is not practical to construct a fixed type
wind-powered generator plant since the cost for constructing the
substructure becomes very high.
[0007] Therefore, when the water is deep, a floating-type
wind-powered generator, in which windmill generator sets are
installed on a floating body, is used.
[0008] An example of a floating-type wind-powered generator plant
is disclosed, for example, in Japanese Unexamined Patent
Publication No. 3-57885.
[0009] For the wind-powered generator plant in the '885
publication, a floating body is built as a framework lying on a
single plane (i.e., truss structure) using steel pipes, and a
plurality of windmill generator sets are installed on the floating
body. The invention of the '885 publication is intended to reduce
the construction cost of a floating body for a floating type
wind-powered generator plant by constructing the floating body as a
truss structure using steel pipes.
[0010] However, when the number of the windmill generator sets
installed on the floating body increases, the cost for constructing
the floating body increases and the unit power generating cost of
the plant becomes excessively high even if a truss structure of
pipes as disclosed in the '885 publication is used for the floating
body.
[0011] When more than two windmill generator sets are used, if the
windmills are disposed close to each other in the direction of the
wind, the power generation efficiency of the downwind windmill
generator set decreases due to the influence of the upwind windmill
generator set. Therefore, when two or more windmill generator sets
are used in a wind-powered generator plant, the interval between
the windmill generator sets adjacent to each other in the direction
of the wind must be sufficiently large. Especially in the case
where the wind direction is not constant, i.e., when daily or
seasonal changes in the wind direction can be expected, the
intervals between the windmills adjacent to each other in all
possible wind direction must be sufficiently large.
[0012] In general, when the distance between the adjacent windmill
generator sets in the wind direction decreases, the power
generation efficiency of the downwind windmill generator set
decreases. The power generation efficiency of a windmill generator
set is defined as a ratio of an amount of electric power generated
by a windmill generator set when it is disposed adjacent to another
windmill generator set and an amount of electric power generated by
the same windmill generator set when it is disposed alone in the
same wind conditions. Therefore, heretofore, it was believed that a
total power generation efficiency of a wind-powered generator plant
rapidly decreases and, thereby, the unit power generating cost of
the wind-powered generator plant as a whole rapidly increases as
the distance between the windmill generator sets in the plant
decreases. A total power generation efficiency of a wind-powered
generator plant is defined as a ratio between an actual amount of
the power generation of the plant as a whole and a sum of the
amounts of the power generation of the respective windmill
generator sets when the respective windmill generators are disposed
alone in the same wind conditions.
[0013] In general, in order to suppress the increase in the unit
power generating cost of the wind-powered generator plant to within
a practical range, the maximum allowable reduction in the total
power generation efficiency of the plant when two or more windmill
generator sets arranged in the direction of the wind is about 20%.
According to a commonly used estimation method for the total power
generation efficiency, it was believed that a distance greater than
four times the diameter of rotors of the windmills would be
required between the centers of the windmills, i.e. the distance
between the hubs of the respective rotors of the windmills must be
larger than four times the rotor diameter in order to keep the
reduction of the total power generation efficiency of the plant
less than 20%.
[0014] In the case where the wind-powered generator plant uses 1
mega-watt class windmill generator sets, the diameter of the rotors
of the windmills is about 60 meters. This requires a minimum of 240
meters between the respective windmill generator sets. A 240 meter
distance between the windmill generator sets does not involve
serious problems in a land-based wind-powered generator plant.
However, in a floating type wind-powered generator plant, the size
of the floating body on which the windmill generator sets are
installed becomes extremely large if the hub distance between the
respective windmill generator sets must be larger than 240 meters.
This causes a serious increase in the construction costs of the
floating body and, even though the decrease in the power generation
efficiency is maintained within the allowable value, the unit power
generating cost of the plant, including the construction cost of
the floating body, becomes excessively high.
SUMMARY OF THE INVENTION
[0015] In view of the problems in the related art as set forth
above, the object of the present invention is to reduce the unit
power generating cost of a floating type wind-powered generator
plant to a practical level by suppressing the increase in the
construction cost of the floating body.
[0016] The objects as set forth above is achieved by a wind-powered
generator plant, according to the present invention, comprising a
floating body placed on a water surface and a plurality of windmill
generator sets disposed on the floating body, wherein at least one
pair of the windmill generator sets are disposed on the floating
body in such a manner that a distance between the center of the
rotors of the windmills is less than four times of the diameter of
the rotors of the windmills.
[0017] According to the present invention, the distances between
the centers of the rotors of the windmills of the windmill
generator sets are set at a value smaller than the conventional
minimum value of four times the rotor diameter.
[0018] When more than two windmill generator sets are installed on
a floating body, particularly in the case where the direction of
the wind changes in accordance with time of the day or time of the
year, the hub distance between the windmill generator sets adjacent
in all direction to each other must be larger than a certain
minimum value (a value required for keeping the reduction of the
power generation efficiency of the windmill generator sets within
an allowable range). Therefore, the upper surface area of the
floating body increases in proportion to a square of the minimum
hub distance. The construction cost of a floating body increases,
for example, in proportion to the upper surface when a box-shaped
floating body is used. Therefore, the construction cost of the
floating body increases in proportion to a square of the hub
distance when a box-shaped floating body is used. When a truss
structure is used for the floating body as disclosed in the '885
publication, although the construction cost can be lower than the
case where a box-shaped floating body is used, the construction
cost of the floating body still increases at a rate larger than a
value proportional to the hub distance and less than a value
proportional to a square of the hub distance.
[0019] In order to reduce the construction cost of the floating
body, therefore, it is necessary to reduce the hub distance.
However, heretofore, it was believed that it is not possible to
reduce the hub distance to a value lower than the minimum distance
of four times the rotor diameter. If the hub distance was reduced
to a value lower than this minimum distance, it was believed that
the increase in unit power generating cost of the plant due to the
decrease in the total power generation efficiency would exceed the
decrease in the construction cost of the floating body.
[0020] As a result of repeated experiments, the inventors found
that the total power generation efficiency of the wind-powered
generator plant does not decrease, as it was believed heretofore,
when the hub distance becomes smaller than four times of the rotor
diameter. It was found by the inventors that, actually, the total
power generation efficiency of the wind-powered generator plant
decreases very slowly as the hub distance decreases, in contrast to
what was believed heretofore, even in the range where the hub
distance is smaller than four times the diameter of the rotor.
[0021] In other words, it was found by the inventors that, although
the total power generation efficiency of the plant decreases as the
hub distance decreases, the increase in the unit power generating
cost due to the decrease in the power generation efficiency is
smaller than the decrease in the unit power generating cost due to
the reduction of the construction cost by reducing the hub
distance. Therefore, in contrast to what was believed heretofore,
it was found that the unit power generating cost of the
wind-powered generator plant can be reduced by reducing the hub
distance to a value less than four times of the rotor of the
windmill.
[0022] In the present invention, based on the findings explained
above, the unit power generating cost of the wind-powered generator
plant is largely lowered by reducing the hub distance between the
windmill generator sets to a value smaller than four times the
diameter of the rotor of the windmill.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The present invention will be better understood from the
description, as set forth hereinafter, with reference to the
accompanying drawings in which:
[0024] FIG. 1 is a schematic perspective view of a floating type
wind-powered generator plant according to an embodiment of the
present invention;
[0025] FIG. 2 shows a relationship between a windmill interval
ratio and a power generation efficiency;
[0026] FIG. 3 shows a relationship between a windmill interval
ratio and a unit power generating cost taking into account the
decrease in the power generation efficiency;
[0027] FIG. 4 is a schematic perspective view of a floating type
wind-powered generator plant according to another embodiment of the
present invention;
[0028] FIG. 5 is a schematic perspective view showing an embodiment
of the present invention which is different from those in FIGS. 1
and 4; and
[0029] FIG. 6 is a schematic perspective view showing another
embodiment of the present invention which is different from those
in FIGS. 1, 4 and 5.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0030] Hereinafter, embodiments of the wind-powered generator plant
according to the present invention will be explained with reference
to FIGS. 1 through 6.
[0031] FIG. 1 is a perspective view showing an embodiment of the
floating type wind-powered generator plant according to the present
invention.
[0032] In FIG. 1, reference numeral 1 designates a floating body
constructed as a structure floating on water, numeral 30 designates
a windmill generator set for power generation. In this embodiment,
the structure forming the floating body is constructed by combining
hollow beam members. Each of the hollow beam members has a
rectangular cross section and, in this embodiment, three beam
members having an identical length are connected to each other in
such a manner that the respective members form a respective side of
an equilateral triangle-shape floating body. On the floating body,
at each of the three corners of the triangle, a windmill generator
set is disposed.
[0033] As can be seen from FIG. 1, each of the windmill generator
sets 30 includes a rotor 31 being rotated by wind and a tower 33
for supporting the rotor 31. The position of the rotor 31 is
controlled so that it turns around the center axis of the tower 31
in response to changes in the wind direction so that the rotor 31
always faces the upwind direction. The rotation of the rotor 31 is
converted into electricity by a generator (not shown) and sent to
the land through an electric power cable.
[0034] The hollow beam members 11 of the floating body, which forms
the respective sides of the triangle, are constructed by welding
steel plates. Each beam member has a rectangular cross section of,
for example, about five meters wide (W in FIG. 1) and eight meters
high (H in FIG. 1). Each structural member 11 is fabricated and
connected to each other in order to form a triangular floating body
1, for example, using a conventional facility such as that of an
existing shipyard. After completing the construction thereof, the
floating body 1 is towed to a plant site where the floating body 1
is fixed by an anchor cable.
[0035] In the embodiment in FIG. 1, the diameter of the rotor 31 (D
in FIG. 1) is about forty-five meters, while the length of each
side of the floating body 1 (L in FIG. 1) is about sixty meters. In
other words, the distance between the centers of the windmills 30
(the distance between the rotor hubs) is set at about 1.3 times of
the rotor diameter.
[0036] As explained before, the total power generation efficiency
of the wind-powered generator plant decreases as the hub distance
between two adjacent windmill generator sets decreases. Heretofore,
it was believed that the power generation efficiency of the
downwind windmill generator set decreases in proportion to the hub
distance to the upwind windmill generator set and the power
generation efficiency of the downwind windmill generator set
decreases to about 80% when the hub distance is about four times of
the rotor diameter. Further, it was believed that the power
generation efficiency continues to decrease in proportion to the
hub distance also in the region where the hub distance is smaller
than four times of the rotor diameter. In general, the maximum
allowable reduction in the power generation efficiency of the
downwind windmill generator sets is about 20% when two or more
windmill generator sets are arranged in the wind direction.
Therefore, it was believed that the allowable minimum hub distance
between the windmill generator sets is about four times of the
rotor diameter and, if the hub distance is smaller than four times
of the rotor diameter, the unit power generating cost of the plant
as a whole increases sharply since the increase of the unit power
generating cost due to the decrease in the power generation
efficiency of the windmill generator sets exceeds the decrease in
the unit power generating cost due to the decrease in the
construction cost of the floating body.
[0037] However, according to the research by the inventors, the
decrease in the power generation efficiency of the downwind
windmill generator sets due to the decrease in the hub distance to
the upwind windmill generator sets is much smaller than was
believed heretofore.
[0038] FIG. 2 is a graph showing the change in the power generation
efficiency due to the change in the hub distance of windmill
generator sets according to the inventors' research. In FIG. 2,
horizontal axis denotes an interval ratio which is defined by the
ratio between the hub distance between the windmill generator sets
and the diameter of the rotor and the vertical axis denotes the
plant power generation efficiency of the plant which is defined by
a ratio between an actual amount of the power generation of the
plant as a whole and a sum of the amounts of the power generation
of the respective windmill generator sets when the respective
windmill generators are disposed alone in the same wind conditions.
The solid line in FIG. 2 shows the result of the inventors'
research and the broken line in FIG. 2 shows a calculated value
based on the conventional estimation method, respectively.
[0039] According to the conventional estimation method, as can be
seen from the broken line in FIG. 2, the total power generation
efficiency decreases in proportion to the interval ratio and, the
total power generation efficiency decreases to the maximum
allowable limit (80%) when the interval ratio decreases to about 4
(i.e., when the hub distance decreases to about four times of the
rotor diameter). Further, in the region where the interval ratio is
smaller than 4, the total power generation efficiency continues to
decrease in proportion to the interval ratio. Thus, when a
plurality of windmill generator sets are to be installed on a
floating body, a minimum of four times the rotor diameter is
required for the hub distance. Therefore, it was believed that the
unit power generating cost could not be reduced by reducing the hub
distance to a value lower than four times of the rotor
diameter.
[0040] In contrast to the conventional estimation method, according
to the inventors' research, based on experiment, indicated by the
solid line in FIG. 2, although the total power generation
efficiency decreases as the interval ratio decreases, the rate of
decrease is much smaller than that of the conventional estimation
method. In addition to that, it was found that the total power
generation efficiency actually changes only slightly in the region
where the interval ratio is between 4.0 and 1.5. As can be seen
from the solid line in FIG. 2, the total power generation
efficiency decreases in accordance with the decrease in the
interval ratio when the interval ratio is less than 1.5.
[0041] Therefore, according to the inventors' research, it was
found that the size of the floating body could be reduced to the
extent where the interval ratio is about 1.5 without any
accompanying substantial decrease in the total power generation
efficiency. This means that the unit power generating cost of the
floating type wind-powered generator plant decreases as the
interval ratio decreases as long as the interval ratio is larger
than about 1.5. However, since the total power generation
efficiency decreases rather steeply as the interval ratio decreases
when the interval ratio is smaller than 1.5, there exist a point
where the increase in the unit power generating cost due to the
reduction in the total power generation efficiency exceeds the
decrease in the unit power generating cost due to the decrease in
the construction cost of the floating body in the region where the
interval ratio is smaller than 1.5. Therefore, it is considered
that an optimum interval ratio where the unit power generating cost
becomes minimum is less than 1.5. Since the interval ratio cannot
be reduced to less than 1.0 in order to avoid interference between
the rotors of neighboring windmills, the optimum interval ratio
exists in the region between 1.5 and 1.0.
[0042] The optimum interval ratio changes according to various
factors such as the location of the plant site, type and shape of
the floating body, wind velocity and the characteristics in the
change of wind direction etc.
[0043] FIG. 3 is a graph showing an example of the relationship
between the unit power generating cost of a floating-type
wind-powered generator plant and the interval ratio of the windmill
generator sets installed thereon. FIG. 3 shows a case where the
triangular floating body made of hollow beam members having
rectangular cross sections, as shown in FIG. 1, is used. The unit
power generating cost is calculated taking into account the
decrease in the total power generation efficiency of the plant due
to a decrease in the hub distance.
[0044] The vertical axis in FIG. 3 denotes a ratio of the unit
power generating cost assuming that the unit power generating cost
is 1.0 when the interval ratio is 2.0 and the horizontal axis
denotes the interval ratio.
[0045] As explained above, the unit power generating cost decreases
as the interval ratio decreases in the region where the interval
ratio is larger than about 1.5 and, becomes minimum at the interval
ratio less than 1.5 (for example, about 1.3). The unit power
generating cost increases as the interval ratio increases when the
interval ratio is less than this point (about 1.3). Therefore, the
optimum interval ratio where the unit power generating cost becomes
minimum is about 1.3 in this case. In the embodiment in FIG. 1, the
interval ratio is set at this optimum value, i.e., the hub distance
between the windmill generator sets (L=60 meters) is set at a value
about 1.3 times of the rotor diameter (D=45 meters).
[0046] Though the total power generation efficiency does not
substantially change in the region where the interval ratio is
larger than 1.5 in the case shown in FIG. 2, the actual interval
ratio where the decrease in the power generation efficiency starts
varies in accordance with wind conditions such as characteristics
of the changes in the velocity and the direction of wind.
[0047] Therefore, taking into account this variation, it is
preferable to set the hub distance between the windmill generator
sets at a value between 1.5 and 2 times the rotor diameter in order
to avoid a relatively large change in the total power generation
efficiency of the plant due to changes in the wind conditions.
[0048] Though the floating body is constructed as a triangular
structure made by combining hollow rectangular cross section beam
members in the embodiment in FIG. 1, a floating body having other
forms can be used in the present invention.
[0049] FIGS. 4 to 6 show examples of floating bodies in other
forms.
[0050] FIG. 4 shows a floating body constructed as a box-like
hollow structure having a rectangular upper face. Windmill
generator sets 30 are disposed on the respective corner of the
rectangular upper face of the floating body. In this case, the hub
distance between two diagonally adjacent windmill generator sets is
larger than the hub distance between two windmill generator sets
arranged along the side of the rectangular. Thus, a sufficiently
large hub distance between two diagonally adjacent windmill
generator sets can be obtained even if the hub distance between two
windmill generator sets arranged along the side of the rectangular
is reduced to minimum distance.
[0051] FIG. 5 shows a floating body having a triangular shape
similar to that of FIG. 1. In this embodiment, however, steel pipes
having circular cross sections are used instead of hollow
rectangular cross section beam members in FIG. 1. In this
embodiment, the construction cost of the floating body is further
reduced by using a truss structure of steel pipes. Further, in the
embodiments in FIGS. 1 and 5, since the floating body has a
triangle contour, the upper area of the floating body divided by
the number of the windmill generator set becomes a minimum, whereby
the construction cost of the floating body is minimized. However,
it is also possible to form a triangular shaped floating body as a
box-like structure similar to that in FIG. 4, instead of truss
structure in FIGS. 1 and 3. Further, as shown in FIG. 6, the
rectangular shaped floating body may be formed as a truss structure
using steel pipes or hollow rectangular cross section beam
members.
[0052] As explained above, according to the present invention, the
unit power generating cost of a floating type wind-powered
generator plant can be largely reduced by disposing more than two
windmill generator sets at a interval smaller than four times the
rotor diameter.
* * * * *